Time filter

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Tai Z.,National Time Service Center | Tai Z.,University of Chinese Academy of Sciences | Yan L.,National Time Service Center | Zhang Y.,National Time Service Center | And 3 more authors.
2016 IEEE International Frequency Control Symposium, IFCS 2016 - Proceedings | Year: 2016

Reduction of residual amplitude modulation (RAM) level induced by electro-optic modulation is important for frequency modulation (FM) technique to reach higher sensitivity. Here, we present a passive approach using a well-designed electro-optic modulator (EOM) to reduce the RAM. Although low RAM could be achieved by critical actively controls of temperature and voltage of a common EOM. This passive approach is more simple, reliable and easier to be realized. We evaluate the performance of such an EOM by comparing system noise level of a standard PDH frequency-stabilization system using this EOM with a commercial one with the addition of a good quality polarizer. RAM depth (versus phase modulation (PM) depth) of this EOM is at 10-6 level. Frequency instability induced by this EOM is below 1×10-16 @ 1s for our cavity-based ultra-stable laser, which is more than one order lower than the other. © 2016 IEEE.


Zhang H.,National Time Service Center | Li H.,National Time Service Center
EFTF 2012 - 2012 European Frequency and Time Forum, Proceedings | Year: 2012

Two-way time and frequency transfer (TWSTFT) is a high precision time transfer because TWSTFT via the GEO satellite can eliminate path delay mostly. Many factors affect the time transfer precision, such as: the modem time delay, the uplink and downlink path delay, a satellite transponder delay and delay of Sagnac effect etc These effects can be measured or calculated. However, Temperature and humidity will reduce the performance of time transfer[1]. Besides, it can not be measured and calculated. In this text, we analyzed several years' TWSTFT data including the temperature and humidity value between NTSC (National Time Service Center) earth station and international earth stations and discussed the correlation between the external environment and TWSTFT comparison result. On the other hand, we did the experiment using satellite simulation, measured the earth stations equipment time delay and recorded the temperature and humidity. In the last, we drew the conclusion with the external environment and TWSTFT comparison result and had the advice to compensate for it. © 2012 IEEE.


Sun H.,Xi'an University of Arts and Science | Yuan H.,National Time Service Center | Zhang H.,National Time Service Center
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control | Year: 2010

The impact of navigation satellite ephemeris error on satellite common-view time transfer was analyzed. The impact varies depending on the angle in view of a satellite relative to a user (elevation) and the baseline distance between 2 users. Some extents of the impact were figured out for several elevations and different baseline. As an example, results from several common-view time transfer links in China via Compass satellite were given. © 2006 IEEE.


Ren Y.,National Time Service Center | Ren Y.,University of Chinese Academy of Sciences | Li X.-H.,National Time Service Center | Xue Y.,National Time Service Center | Dong R.,National Time Service Center
IFCS 2014 - 2014 IEEE International Frequency Control Symposium, Proceedings | Year: 2014

In order to steer master clock in timekeeping laboratory, it is necessary to identify a suitable algorithm for steering UTC(Lab) to UTC for a period of 45 days. By introducing Kalman Filter into the steering, some considerations which are assumed to effect result are encountered. By compared with the result of quadratic polynomial model, Kalman Filter, based on four years historical data and state parameter initialed by 4 order quadratic polynomial model, is able to predict the plausible results in terms of both stability and accuracy. © 2014 IEEE.


Xu B.,Nanjing University | Wang Y.,Aerospace System Engineering Shanghai | Yang X.,National Time Service Center
Studies in Computational Intelligence | Year: 2013

In order to improve navigation satellite clock error prediction accuracy, a hybrid model is proposed in this paper. According to the physics property of atomic clock, the model firstly fits the clock error series by polynomial model. Then it models for polynomial fitting residuals, using functional network. The functional network structure is defined by wavelet de-noising and phase space reconstruction. Finally the GPS satellites are taken for example and four separate predict tests are done, the simulation results show that the proposed method can fit and predict the clock error series effectively, whose predict accuracy is better than those of IGU-P and conventional methods. © Springer-Verlag Berlin Heidelberg 2013.


Xu B.,Nanjing University | Wang Y.,Shanghai Aerospace System Engineering | Yang X.,National Time Service Center
Neural Processing Letters | Year: 2013

The high precision prediction of atomic clocks on board is a key technology for the long-term autonomous operation of a navigation satellite system. Some researches show that the performance of traditional prediction models of atomic clocks can not meet the requirements of practical applications. In order to improve the atomic clock error prediction accuracy, we propose a model based on functional network in this paper. According to the data characteristics of atomic clocks, the clock error series is firstly fit by polynomial and then the residuals is modeled by functional network. Finally, by using the data of GPS satellites, five independent prediction tests have been done to verify the model. The simulation results show that, compared with the traditional models, the proposed model can fit and predict clock error more effectively. © 2012 Springer Science+Business Media New York.


Yao Y.,Xian University of Posts and Telecommunications | Yao Y.,University of Chinese Academy of Sciences | Zhang S.G.,National Time Service Center
Applied Mechanics and Materials | Year: 2014

This paper proposed two kinds of precepts on time comparison for SDH network in practice. The precepts are the method of double-end bi-directional and the method of single-ended one-way. The computational model and network configuration of those precepts are given in this paper. Through the first precept, the time delay of fiber transferring can be got also, so the method can be used to time deliver too. © (2014) Trans Tech Publications, Switzerland.


Tai Z.,National Time Service Center | Tai Z.,University of Chinese Academy of Sciences | Yan L.,National Time Service Center | Zhang Y.,National Time Service Center | And 3 more authors.
2016 European Frequency and Time Forum, EFTF 2016 | Year: 2016

Reduction of residual amplitude modulation (RAM) level induced by electro-optic modulation is important for frequency modulation (FM) technique to reach higher sensitivity. Here, we present a passive approach to make a well-designed electro-optic modulator (EOM) with ultra-low RAM. Although low RAM could be achieved by critical actively controls of temperature and voltage of a common EOM. This passive approach is more simple, reliable and easier to be realized. We evaluate performance of such an EOM by comparing system noise level of a standard PDH frequency-stabilization system using this EOM with a commercial one with the addition of a good quality polarizer. RAM depth (versus phase modulation (PM) depth) of this EOM is at 10-6 level. Frequency instability induced by this EOM is below 1×10-16 @ 1s, which is more than one order lower than the other. © 2016 IEEE.


Lu J.,Beijing Institute of Technology | Ren Y.,National Time Service Center | Li X.,National Time Service Center | Liu Y.,National Time Service Center | Zhang S.,National Time Service Center
2015 Joint Conference of the IEEE International Frequency Control Symposium and the European Frequency and Time Forum, FCS 2015 - Proceedings | Year: 2015

As same as other satellite navigation systems, the time difference is considered as one of the basic observations in Beidou satellite navigation system. Therefore, an accurate and stable system time is crucial to realize the system function. Based on the inverse decomposition method, this paper analyzes the requirements of Beidou system time (BDT) on behalf of the Beidou System service. Three time transfer links, The Two-Way Satellite Time transfer, GPS Common-View Time Comparison and Beidou Common-View Time Comparison, are established between National Time Service Center and the Beidou system time center in order to obtain the time difference between BDT and UTC(NTSC). At last, the accuracy and stability of BDT are discussed based on the performance of these three links © 2015 IEEE.


Wang Y.,Nanjing University of Aeronautics and Astronautics | Xu B.,Nanjing University of Aeronautics and Astronautics | Xu B.,Nanjing University | Yang X.-H.,National Time Service Center
Yuhang Xuebao/Journal of Astronautics | Year: 2012

In order to improve the prediction accuracy and real-time performance of the navigation satellite clock error, a satellite clock error prediction method based on the combination of polynomial model and functional network is proposed in this paper. Firstly a polynomial model is used to fit the clock error series according to its physical property, and then the polynomial fitting residual is modeled based on the functional network, while the functional network structure is defined by using wavelet denoising and phase space reconstruction. Finally the GPS satellites are taken for example and four short-term prediction tests are done, and the simulation results show that the proposed method can be used to fit and predict the clock error series effectively, whose prediction accuracy is better than that of IGU-P ephemeris.

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